Six MS-patients were inoculated three times with autologous attenuated MBP-specific T cell clones at two month intervals. No toxic effects were observed. After the third inoculation the precursor frequency of the MBP-specific T cells dropped to undetectable levels in all patients. Injection of attenuated MBP-specific T cells gave rise to a pronounced response of anti-clonotypic T cells and a limited anti-ergotypic response. The anti-clonotypic T cells proliferated in the presence of the vaccine clones and were inhibitory and cytotoxic for the same vaccine clones. This clinical trial shows for the first time that antigen specific T cell vaccination in humans is feasible. The results obtained are highly promising for future treatments of Multiple Sclerosis and other autoimmune diseases.